This invention refers to a magnetron sputtering cathode of the type which has a target plate of the material to be sputtered connected to a support body of non-magnetic material, a chamber disposed between the support body and the target plate, coolant flowing through the chamber, and the chamber formed by a recess in the support body, the recess being tightly covered by the target plate, and a permanent magnet system disposed beneath the target plate.
Such a magnetron sputtering cathode is a component of an apparatus for coating substrates, with the coating material in each case, here the target material, being precipitated from the gas phase onto the substrate to be coated. The target material is converted to the gas phase by sputtering. In this sputtering process, material is knocked from the target by ion bombardment of the target. The ions required for the sputtering process are generally produced by collisions of gas atoms and electrons in a glow discharge and are accelerated into the target forming the cathode with the aid of an electric field. The substrates, arranged at suitable locations, catch the atoms knocked out of the target material and in this way are coated with the target material.
In a magnetron sputtering cathode such as that mentioned above, a magnetic field is used to encompass the glow discharge plasma and thereby to lengthen the path of the electrons, so that the collision rate of gas atoms and electrons is increased. By this means a sputtering yield higher than in apparatus working without magnetic restriction occurs. Furthermore, the sputtering process can be carried out with a substantially lower gas pressure.
The magnet system of known magnetron sputtering cathodes is generally designed with a circular or annular discharge area formed on the target plate. A considerable disadvantage of these known cathodes is that the cathode width is limited by the realizable width of the target erosion zone. By target erosion zone the discharge area on the target surface is meant, i.e. the area in which the target material is effectively sputtered off. The width of this target erosion zone depends primarily on the spacing of the magnetic poles, but also on the distance between the magnet system and the target surface. These distances can not be altered arbitrarily, as the erosion profile becomes less favorable with increasing distance between the magnetic poles, due to the lessening stength of the magnetic field. This limited cathode width makes the even coating of a larger workpiece or a plurality of workpieces considerably more difficult. The arrangement of several of the known magnetron sputtering cathodes adjacently does improve the coating conditions; however, each cathode needs its own power supply, whereby this solution becomes extremely costly. A further disadvantage of the known magnetron sputtering cathode is that due to the circular or annular form of the target erosion zone, only a small portion of the entire target plate can be exploited for the sputtering.
Also, the necessary and efficient cooling of the target plate and of the magnet system presents a further problem with these known cathodes. For example, in the cathode described above, a direct cooling of the back side of the target plate is provided; however, cooling takes place only in the direct area of the annular errosion zone by means of a turbulently flowing coolant. In order to achieve adequate movement of the coolant and to prevent the coolant from coming to a standstill in remote corners, a correspondingly high coolant pressure must be selected. This results in a relatively large difference between the pressure in the cooling chamber and the pressure in the vacuum chamber surrounding it, so that target distortion or ruptures in the target material can not be ruled out. To avoid this, the known magnetron sputtering cathode can only be operated with relatively low cathode output.